1. Technical Field
The present invention relates to a tape drive member suitably adapted as a capstan of, for example, a tape recorder and to a manufacturing method for the same, and more particularly, to a tape drive member which is capable of driving a tape in a stable and reliable manner.
2. Background Art
As is well known, a capstan of a tape recorder as an example of a tape drive member is supported in the manner shown in FIG. 1. Referring to FIG. 1, reference numeral 11 denotes a main chassis of a tape recorder which has a through-hole 111, formed at a predetermined position thereof, through which extends a support cylinder 12. A flange 121 is formed substantially midway along the support cylinder 12. Screws 13 are respectively inserted into through-holes 122 and threadably engage with screw holes 112 formed in the main chassis 11. In this manner, the support cylinder 12 is fixed onto the main chassis 11.
A capstan 14 extends through the support cylinder 12. The capstan 14 rotates with a flywheel since its lower portion is inserted and fixed in a through-hole 151 formed at the center of rotation of the flywheel 15. The capstan 14 is supported by support members 16 and 17 which are arranged at the upper and lower ends, respectively, of the support cylinder 12 so that the capstan 14 may rotate smoothly without jolting. The lower end of the capstan 14 is in contact with a bearing 19 of a subchassis 18 which is arranged substantially parallel to the main chassis 11. The flywheel 15 is coupled through a belt 20 to a motor (not shown) to be driven thereby.
A pinch roller 22 is urged against the upper portion (FIG. 1) of the capstan 14 in putting a tape 21 therebetween. The pinch roller 22 is rotatably mounted through a support member 26 on a shaft 24 extending from a slider 23 which is slidable in the directions indicated by arrows A and B in synchronism with the operation of a tape constant speed drive member (not shown). In the tape drive stop state, the rotational force of the motor as described above is transmitted to the flywheel 15 and the capstan 14, which rotate stably. However, since the slider 23 has been moved in the direction indicated by arrow B and the pinch roller 22 is separated from the capstan 14, the tape 21 is not driven. When the tape constant speed drive member is operated in the tape drive state, the slider 23 is synchronously slid in the direction indicated by arrow A. Then, the pinch roller 24 is urged against the rotating capstan 14 in putting the tape 21 therebetween, as shown enlarged in FIGS. 2(a) and 2(b), and the tape 21 is driven.
The driving force F for driving the tape 21 by the capstan 14 may be approximately given by the following equation: EQU F=(.mu.1+.mu.2)P
where
.mu.1 is the friction coefficient between the tape 21 and the pinch roller 22; PA1 .mu.2 is the friction coefficient between the tape 21 and the capstan 14; and PA1 P is the pinching force acting on the tape 21.
It may be seen from this equation that, if the pinching force P remains constant, the friction coefficients .mu.1 and .mu.2 must be increased in order to obtain a greater driving force F, thereby driving the tape 21 in a stable and reliable manner.
Meanwhile, the portion of the capstan 14 which is supported by the support cylinder 12 through the support members 16 and 17 preferably cause low friction to ensure smooth rotation. On the other hand, the tape driving portion of the capstan 14 to which the pinch roller 22 is urged must have a high friction coefficient.
For this reason, a conventional capstan 14 is made of stainless steel which is ternary alloy of iron (Fe), chrome (Cr) and nickel (Ni) as major components to have a smooth surface with a small friction coefficient. The tape driving portion of the capstan 14 which will be brought into contact with the tape 21 is treated by sand blasting or the like. According to the sand blasting treatment, fine hard particles (e.g., of a ceramic) are collided at high speed against the tape driving portion of the capstan 14 so as to abrade the tape driving portion to a rough surface 26 as shown in FIG. 3. When the pinch roller 22 is urged against the rough surfaced tape driving portion 26 of the capstan 14 in putting the tape 21 therebetween, the friction coefficient .mu.1 between the tape 21 and the pinch roller 22 and the friction coefficient .mu.2 between the tape 21 and the capstan 14 are increased, so that a greater driving force F is obtained.
However, the conventional tape drive member and the method for manufacturing the same as described above are subject to drawbacks to be described below. The surface of the capstan 14 which has been treated by sand blasting has fine cracks or distortion as seen in the microphotograph (1,000 magnification) shown in FIG. 5. Therefore, the cracked or distorted part of the capstan 14 becomes worn down by the tape 21 with frequency of use. Then, the driving force F is weakened, and the initial performance cannot be maintained for a prolonged period of time, resulting in poor durability. The respective components of iron, chrome and nickel as described above are randomly exposed to the surface of the capstan which was treated by sand blasting. Since iron is softer than chrome, nickel or the like, it is worn out more quickly upon contact with tape 21, also resulting in poor durability. As described above, fine hard particles are collided against the tape drive portion of the capstan 14. Therefore, as shown in FIG. 3, the diameter of the rough surface portion 26 of the capstan 14 which has been subjected to sand blasting is smaller than the remaining portion of the capstan 14 which was not subjected to sand blasting. Consequently, the rough surface portion 26 becomes eccentric with respect to the axis of the remaining portion of the capstan 14.